It was supposed to be Jose Mourinho's celebratory return to Champions League football as a Chelsea manager. After 90 minutes of action at Stamford Bridge it turned out to be a bit of a nightmare as FC Basel came from behind to upset Chelsea 2-1. Lionel Messi and Barcelona oozed class as the Argentine superstar struck a hat-trick in an authoritative 4-0 win over Ajax, while Arsenal began their campaign in impressive fashion with a 2-1 victory over Marseille.

Barcelona forward Lionel Messi celebrates after scoring against Ajax in the Champions League, September 18, 2013Reuters

It was supposed to be Jose Mourinho's celebratory return to Champions League football as a Chelsea manager. After 90 minutes of action at Stamford Bridge it turned out to be a bit of a nightmare as FC Basel came from behind to upset Chelsea 2-1.

Lionel Messi and Barcelona oozed class as the Argentine superstar struck a hat-trick in an authoritative 4-0 win over Ajax, while Arsenal began their campaign in impressive fashion with a hard-fought 2-1 victory over Marseille.

At Stamford Bridge, the home fans did not see a great deal of dominance from Chelsea, but the Blues did manage to get the go-ahead goal just before halftime.

As the half wore on, Chelsea kept pressing and probing with Eden Hazard, in particular looking lively, while Willian did not have the most influential of games on his debut.

For Basel Mohamed Salah was the most dangerous player, with the winger threatening Chelsea's goal time and again with some searing runs.

However, after a period of play where neither team could really break through, Chelsea finally found their goal through the excellent Oscar.

David Luiz made a run down the middle before passing for Frank Lampard, who in turn teed up Oscar to smash it into the bottom corner.

However, the game turned on its head in the final 20 minutes with Basel stunning Chelsea and the home crowd with two goals in the space of ten minutes.

It was no surprise that the first goal was scored by Salah, who had a wonderful game for the Swiss side, with the winger bending one brilliantly into the back of the net in the 71st minute after some brilliant team play.

Basel took the lead ten minutes later when Marco Streller headed the ball in at the near post as a look of disbelief crept into the face of Mourinho.

Schalke scored an authoritative 3-0 win over Steaua Bucharest in the other Group E game, thanks to goals from Atsuto Uchida, Kevin-Prince Boateng and Julian Draxler.

At the Stade de Gerland, Marseille were the much better team in the first half with Arsenal failing to find any kind of momentum.

Marseille overran the midfield with their power, outmuscling the Arsenal players and not giving the creative duo of Jack Wilshere and Mesut Ozil any time on the ball whatsoever.

The French side, roared on by a boisterous crowd, looked the more dangerous team going forward as well with Mathieu Valbuena posing a constant threat while Andre-Pierre Gignac might have had a first half goal had it not been for him being caught offside on a number of occasions.

Marseille came close a couple of times with Andre Ayew, who also had a good game, directing a header just wide of the post with Wojciech Szczesny well beaten while Gignac also had a half-chance off a corner.

At the other end, Olivier Giroud did not receive his usual unrelenting service in the first half and therefore could not add to his brilliant record so far this season.

The closest Arsenal came was when Theo Walcott broke free early on, but decided to stay on his feet under the challenge of Jeremy Morel before shanking his shot - the Arsenal forward will probably be ruing having not gone down there inside the box.

Kieran Gibbs came really close early in the second half, but Marseille goalkeeper Steve Mandanda was up to the task making a smart save as Arsenal looked to take control early.

The goal finally did come for Arsenal in the 65th minute and what a goal it was. Gibbs' cross from the left was not cleared by Jeremy Morel, with Theo Walcott taking full advantage smashing a thunderous volley into the back of the net.

Aaron Ramsey continued his stunning form with a goal of some quality late on, but Marseille were given a glimmer of hope with Jordan Ayew scoring from the spot after Ramsey was penalized for a tackle inside the box. Arsenal, though, held on to pick up an impressive and vital win.

In the other game of Group F, Borussia Dortmund fell 2-1 to Napoli with Gonzalo Higuain and Lorenzo Insigne scoring the goals for the Italian side, while the German side's goalkeeper Roman Weidenfeller was sent off in the first half.

At the Camp Nou, the audience were treated to a nice open game with that man again Lionel Messi making all the difference.

Both sides chose to play their passing enterprising football with Ajax hardly intimidated by the stature of their opponents in the first ever European match between the two sides.

Barca took the lead through their talisman, with Messi smashing a powerful freekick beyond Kenneth Vermeer - it was not one of those where he jinked it perfectly over the wall. This strike was hit towards the side of the goalkeeper, but it just had too much venom in it as it cannoned into the net off the inside of the post.

Messi added his second early in the second period with a trademark finish. Sergio Busquets played the little Argentine in on the left-hand channel, with Messi cutting in immediately onto his left foot before slotting it calmly in.

The Barcelona superstar nearly had his hat-trick soon after, but his first-time strike off a pass from Neymar just crept wide, much to the relief of Ajax goalkeeper.

It was game, set and match to Barcelona in the 69th minute with Gerard Pique heading in a splendid cross from Neymar.

On 75 minutes, Messi completed his hat-trick with a remarkably assured finish and with it matching Cristiano Ronaldo's three-goal haul a day ago.

Ajax's night went from bad to worse when Kolbeinn Sigthorsson failed to find the back of the net from the penalty spot with Victor Valdes making a great save.

AC Milan also got off to a bright start with a 2-0 victory over Celtic at the San Siro, with both goals coming in the final ten minutes.